Heat exchanger

ABSTRACT

A heat exchanger includes number of bolted flanges and a number of heat pipes for heating and cooling liquids entering the heat exchanger. One of the bolted flanges connects a plenum housing to a relief valve piping. The relief valve piping remains closed during normal operation of the heat exchanger and opens to maintain pressure when operating pressure of the heat pipes increases above an acceptable level. The heat exchanger also includes a plenum plate, attached to a cold-side housing and the plenum housing, which seals a cold side of the heat exchanger from an upper plenum. The heat exchanger also includes a separation plate, connected to a cold-side housing and the hot-side exit vapor belt, which seals a cold side of the heat exchanger from a hot side of the heat exchanger.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/107,003, filed Jan. 23, 2015, the entirecontents of which are herein incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to heat exchangers, powergeneration, and heat recovery, including waste heat recovery. Moreparticularly, the present disclosure relates to a thermosyphon heatexchanger.

BACKGROUND

Organic Rankine Cycle (“ORC”) power plants exhibit high capital costsrelative to other types of power plants. A substantial portion of thecost of an ORC power plant is attributed to the use of a secondary fluidsystem, which is needed to transfer heat from the heat source to therefrigerant working fluid. Direct heating of the working fluid (e.g.,use of a direct evaporator to eliminate the secondary fluid system) isnot cost-effective with traditional heat exchangers as the resultingexchangers are large and costly. Direct heating also carries theadditional complication for high temperature heat sources of overheatingthe refrigerant to the point of decomposition. In addition to addingsubstantial cost to the ORC power plant, the secondary fluid systemrequires a significant parasitic electrical load to run the circulatingpump(s) for the secondary fluid.

Additionally, multiple other heat exchanger applications suffer fromhigh exchanger costs due to the low area-specific heat transfer rate ofthese exchangers (such as, for example, shell and tube heat exchangers).One such heat exchanger application is district heating, where wasteheat such as engine exhaust is used to provide hot water in populationcenters. These applications include the situation where the cold fluidbeing heated must not exceed a specific temperature due todecomposition, flammability, evaporation, or some other reason.

Further problems exist with thermosyphon (wickless heat pipe) heatexchangers and heat pipe heat exchangers. Thermosyphons and heat pipesare typically implemented as individual sealed tubes or pipes that areclosed at both ends, and which transfer heat via the circulation of aninternal working fluid that evaporates in the hot end segment (where itcools objects or media external to the thermosyphon/heat pipe) andcondenses in the cold end segment (where it heats objects or mediaexternal to the thermosyphon/heat pipe, and where the objects or mediain the cold end segment are at lower temperature than the objects ormedia in the hot end segment). Such exchangers are high in cost due tothe need to fill and seal each thermosyphon/heat pipe individually.Also, the charge cannot be cost-effectively tuned or adjusted due to thelarge number of thermosyphons/heat pipes in the exchanger. Additionally,in high temperature applications, the thermosyphons/heat pipes must bedesigned not only for design condition pressures, but also must bedesigned to withstand the very high pressures that would result fromoperating at maximum possible operating temperature (i.e. thetemperature of the incoming hot flow, for the case where there is a lossof cold-side fluid flow), due to a completely sealed design. This higherdesign pressure requirement then results in thicker walls for thethermosyphons/heat pipes than if they were designed only for the designoperating conditions, increasing cost and reducing heat transfer. Yetanother problem with thermosyphons/heat pipe heat exchangers is that,when the charge is selected to achieve a target dry-out temperature, therequired charge to achieve the target dry-out temperature is often notoptimal for heat transfer. Finally, for some common working fluids suchas water, the use of low cost materials such as stainless steel isgenerally considered unacceptable due to the buildup of non-condensablegases from the reaction of the water with the thermosyphon/heat pipematerials over time, such that the resulting non-condensable gasesoccupy significant volume in the condensing section of thethermosyphon/heat pipe, reducing the effective condenser length andsurface area, and reducing the performance of the thermosyphon/heatpipe. Therefore, there is a need for a heat exchanger system that solvesthe problems in the art.

SUMMARY

The following presents a simplified summary of the disclosure in orderto provide a basic understanding of some aspects of the disclosure. Thissummary is not an extensive overview of the disclosure. It is intendedto neither identify key or critical elements of the disclosure nordelineate the scope of the system and method disclosed herein. Its solepurpose is to present some concepts of the disclosure in a simplifiedform as a prelude to the more detailed description that is presentedlater.

In one embodiment, a heat pipe heat exchanger includes thermosyphon/heatpipes open at the top to a common plenum located above thethermospyhons/heat pipes. This implementation allows for charging alltubes simultaneously (which results in lower cost); allows forcost-effective charge adjustment; allows for use of tube and workingfluid material combinations considered incompatible due to buildup ofnon-condensable gases (for example, plenum provides a volume to collectthese gases without reducing condenser section lengths and activecold-side surface area); and allows for reduction in the required vacuumfor charging when using vacuum charging (for example, due to plenumvolume being available to contain non-evacuated gases).

In one embodiment, a pressure relief system is provided on the plenum.This implementation allows for lower design pressure in high-temperatureapplications, since the design pressure is set by the relief pressureand not the maximum possible pressure resulting from a sealed systemoperating at maximum hot-side temperature, and reduces tube wallthickness and increases heat transfer, both of which reduce cost. Thisimplementation also allows independent control of both thermosyphon/heatpipe charge, and dry-out temperature, so that the charge may be set formaximum heat transfer, and the dry-out temperature set (via the reliefsystem lift pressure) to limit cold-side fluid temperature to a specificvalue regardless of charge.

In one embodiment, a hot-side housing and vapor belts are arranged suchas to achieve uniform flow distribution at the hot inlet via controlleddiffusion, circumferential feed, and even pressurization of the tubebundle via the hot inlet vapor belt. This implementation also results inuniform flow distribution at the hot exit vapor belt via consistent flowturning and pressure loss around the circumference of the hot exit vaporbelt, low pressure loss, and further results in a compact, low-costarrangement.

The following description and the annexed drawings set forth in detailcertain illustrative aspects of the disclosure. These aspects areindicative, however, of but a few of the various ways in which theprinciples of the system and method disclosed herein may be employed andthe system and method disclosed herein is intended to include all suchaspects and their equivalents. Other advantages and novel features ofthe system and method disclosed herein will become apparent from thefollowing detailed description of the system and method disclosed hereinwhen considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a thermosyphon heat exchanger in accordance with oneembodiment; and

FIG. 2 illustrates an internal view of a thermosyphon heat exchanger inaccordance with one embodiment.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The system and method disclosed herein will now be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred implementations of the system and method disclosed herein areshown. The system and method disclosed herein may, however, beimplemented in many different forms and should not be construed aslimited to the implementations set forth herein. Rather, theseimplementations are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the system and methoddisclosed herein to those skilled in the art.

ORC power plants are employed as a means to convert waste heat intoelectricity, typically where the heat source is either too small or toolow in temperature to cost-effectively employ a steam turbine powerplant. For the case where the heat source is of high temperature such asengine exhaust, gas turbine exhaust, incinerators, or biomass boilers,there lies an additional concern when using common ORC working fluids,as they decompose at temperatures well below the temperature of the heatsource. The current solution to the problem is to use a secondary fluidloop to transfer heat from the heat source to the ORC power plant. Thissecondary fluid loop represents a large portion of the cost of the ORCpower plant, and reduces the performance due to the power requirement ofthe circulation pump(s) and heat losses in the secondary fluid loopsystem. Embodiments of the present invention allow for reduction incost, complexity, and physical size of ORC power plants, whileincreasing performance, by replacing the entire secondary fluid loopsystem, along with the heat exchangers on both sides of the secondaryfluid loop (i.e., the heat exchangers transferring heat from the heatsource to the secondary working fluid, along with the heat exchangerstransferring heat from the secondary working fluid to the ORC workingfluid), with a single heat exchanger in accordance with one embodiment.The result is an ORC power plant that is lower in cost, higher inperformance, and is more compact than existing ORC power plants. Thesebenefits then allow for more integration with the heat source, forfurther benefits in cost and performance.

In the present disclosure, the term “thermosyphons/heat pipes” is usedto refer to thermosyphons (wickless heat pipes) or heat pipes (whichhave a wick). Embodiments of the present invention may be implemented byusing thermosyphons or heat pipes. Embodiments of the subject inventionsolve all the above problems of ORC secondary fluid systems, traditionalheat exchangers, and thermosyphon/heat pipe heat exchangers, via athermosyphon/heat pipe heat exchanger that leverages the very highsurface area-specific heat transfer rates of thermosyphons/heat pipes toprovide a compact heat exchanger with lower cost than traditional heatexchangers, and in which the thermosyphons/heat pipes may be open on thetop end to a common plenum that allows for simultaneous charging of allthe thermosyphons/heat pipes. This lowers the time and cost of chargingthe thermosyphons/heat pipes, and also allows for cost-effectiveadjustment of the charge in the field.

Additionally, in one embodiment a pressure relief valve, pressure safetyvalve, or pressure relief system may be placed on the common plenum towhich all thermosyphons/heat pipes are open, which results insignificant reduction in maximum design pressure requirements for thethermosyphons/heat pipes in high temperature applications. This reducesrequired thermosyphon/heat pipe wall thickness which then results inincreased heat transfer, and both reduced wall thickness and increasedheat transfer then contribute to lower cost. It also allows forindependent selection of both the optimal charge for heat transfer, andthe dry-out temperature, since the dry-out temperature is set by therelief pressure and is independent of the charge. In one embodiment, thecommon plenum also creates a volume in which non-condensable gases cancollect without impact to the performance of the thermosyphons/heatpipes, such that previously-unacceptable low-cost materials can be usedwithout negative impact to the performance of the heat exchanger.

Embodiments of the subject invention also resolve issues with use of adirect evaporator in ORC power plants, thereby reducing the cost andincreasing the output of such plants. In addition to the advantagesidentified above, embodiments of the subject invention have thecapability to prevent the overheating and decomposition of the ORCworking fluid. This may be accomplished by setting the relief pressurefor the pressure relief valve, pressure safety valve, or pressure reliefsystem such that the pressure in the thermospyhons/heat pipes does notexceed a pre-determined value, in accordance with one embodiment. As thetemperature in the thermosyphons/heat pipes is a function of workingfluid chemistry, amount of working fluid installed in thethermosyphons/heat pipes (charge), and the pressure of the working fluidin the thermosyphons/heat pipes, the maximum temperature of the workingfluid in the heat pipes may then be limited by the pressure reliefvalve, pressure safety valve, or pressure relief system. In accordancewith one embodiment, the relief pressure may be set within the pressurerange wherein the thermosyphons/heat pipes are actively exchanging heat,and the working fluid is in the two-phase region. In one embodimentwhere the working fluid pressure in the thermosyphons/heat pipes nears,equals, or exceeds the maximum allowable pressure (and correspondingtemperature for working fluid chemistry and charge) for proper operationor at which the equipment is allowed to operate continuously, theresulting release of working fluid by the pressure relief valve,pressure safety valve, or pressure relief system will result inreduction in thermosyphon/heat pipe charge while maintaining theoperating pressure and temperature in the thermosyphons/heat pipes atacceptable levels. This reduction in charge may continue for as long asthe pressure in the thermosyphons/heat pipes remains near the maximumallowable pressure, such that the pressure relief system continues toflow. In the case where the pressure relief system continues to flowuntil the working fluid is completely vaporized (dry-out), heat transferbetween the hot and cold sides of the exchanger will then be essentiallyhalted, as described below in accordance with one embodiment.

The thermosyphon/heat pipe working fluid and charge may be set such thatthe charge is completely vaporized at a pre-determined temperature(known in the art as the dry-out temperature). In the case that thetemperature inside the thermosyphons/heat pipes reaches the dry-outtemperature, the working fluid inside the thermosyphons/heat pipes, andin the common plenum cavity, is completely vaporized, and the heattransfer mechanism of the thermosyphons/heat pipes is then effectivelyturned off, as no liquid condensate returns to the evaporator section ofthe thermosyphons/heat pipes, essentially stopping any further heattransfer. An embodiment utilizes a pressure relief valve, pressuresafety valve, or pressure relief system that allows for dry-out to beattained, as described above, at a desired pressure and temperaturecombination for any given charge, thereby allowing independent controlover both the charge and the dry-out temperature in the design. This isadvantageous since the heat transfer characteristics of thethermosyphons/heat pipes may not be optimal at the charge required bythe desired dry-out temperature in a sealed thermosyphon/heat pipesystem.

The relief pressure may be set below, at, or above the dry-outtemperature of the selected working fluid and charge. Therefore, therelief pressure setting and/or the dry-out temperature may be set suchthat the working fluid remains below the decomposition temperature ofthe ORC working fluid. This prevents the possibility of overheating theORC working fluid as the thermosyphons/heat pipes will not transfer anysignificant heat once the dry-out temperature is reached inside thethermosyphons/heat pipes. Since the exchanger cold-side fluid is heatedalmost exclusively by the thermosyphons/heat pipes, and not directlyreceiving significant heat from the exchanger hot fluid (except at theseparation plate, where reduced hot-side temperatures will exist in thecase of hot fluid exit at the upper hot-side connection, or which can beinsulated as needed to prevent direct heat transfer), in one embodimentthe exchanger cold-side fluid is substantially isolated thermally fromthe hot-side fluid and the heat transfer is controlled passively by thethermosyphons/heat pipes.

An embodiment of the subject invention similarly resolves theabove-identified issues for multiple other heat exchanger applications,via an exchanger with much lower cost than traditional heat exchangers,due to the high surface area-specific heat transfer rate of thethermosyphons/heat pipes, while providing a flexible means to protectthe cold-side fluids from excessive temperatures. Additionally, thecharge and fluid of the thermosyphons/heat pipes can be set such thatthe thermosyphon/heat pipe working fluid freezes at a pre-determinedtemperature set by the charge, which effectively turns off the heattransfer at and below this temperature. As with the relief pressuresetting and dry-out temperature, this can be used for any number ofpurposes including protection of hot and/or cold-side exchanger fluids,or to limit heat transfer directly. Application of embodiments of theinvention in the implementations described above may result in lowerpressure loss due to low fluid velocities on both hot and cold sides ofthe exchanger.

FIG. 1 illustrates a thermosyphon/heat pipe heat exchanger in accordancewith one embodiment. The heat exchanger illustrated in FIG. 1 includesRelief Valve Piping 1, Bolted Flange 2, Plenum Housing 3, Bolted Flange4, Cold-Side Housing 5, Bolted Flange 6, Bolted Flange 7, Hot-SideHousing 8, Bolted Flange 9, Hot-Side Housing Exit Vapor Belt 10, andHot-Side Housing Inlet Vapor Belt 11.

The Relief Valve Piping 1 may be implemented as piping for conveyance ofpressurized fluids, such as piping in compliance with American NationalStandards Institute (ANSI) specifications. Bolted Flange 2 may beimplemented as a piping flange such as piping flange in compliance withAmerican Society of Mechanical Engineers (ASME), ANSI, Thermal ExchangerManufacturing Association (TEMA), or metric nominal diameter (DN) flangespecifications, and may include a gasket for sealing. Plenum Housing 3may be implemented as a pressure vessel enclosing and sealing an openplenum that connects substantially (e.g., enough to freely communicateflow and pressure between the tubes and the plenum) thethermosyphons/heat pipes at the top end. Bolted Flange 4 may beimplemented as a piping flange, such as piping flange in compliance withASME, ANSI, TEMA, or metric DN flange specifications, and may include agasket for sealing. Cold-Side Housing 5 may be implemented as a pressurevessel which may also be made from standard pressure piping, such asANSI, or from rolled sheet, and which may enclose and seal the cold-sideflow volume of the exchanger, may provide inlet and exit piping for thecold-side fluid flow, and may include an expansion joint to alleviatethermal stresses. Bolted Flange 6 may be implemented as a piping flange,such as piping flange in compliance with ASME, ANSI, TEMA, or metric DNflange specifications, and may include a gasket for sealing. BoltedFlange 7 may be implemented as a piping flange, such as piping flange incompliance with ASME, ANSI, TEMA, or metric DN flange specifications,may include a gasket for sealing, or may be clamped or may include anysuitable means of conveyance. Hot-Side Housing 8 may be implemented as apressure vessel which may also be made from pressure piping, such asANSI, or from rolled sheet, and which may enclose and seal the hot-sideflow volume of the exchanger. Bolted Flange 9 may be implemented as apiping flange, such as ASME, ANSI, TEMA, or metric DN flange, and mayinclude a gasket for sealing, or may be clamped or may include anysuitable means of conveyance. Hot-Side Housing Exit Vapor Belt 10 may beimplemented as a pressure vessel which may also be made from pressurepiping, such as ANSI, or from rolled sheet, may enclose and seal thehot-side flow volume of the exchanger near the exit, and may provide foreven flow distribution to the exit piping for the hot-side fluid flow.Hot-Side Housing Inlet Vapor Belt 11 may be implemented as a pressurevessel which may also be made from pressure piping, such as ANSI, orrolled sheet, and/or stamped sheet, may enclose and seal the hot-sideflow volume of the exchanger near the inlet, and may provide for evenhot-side flow distribution to the thermosyphons/heat pipes.

Operation of the heat exchanger illustrated in FIG. 1 operates asfollows, in accordance with one embodiment. Hot fluid enters throughBolted Flange 9, is distributed by Hot-Side Housing Inlet Vapor Belt 11for optimal flow distribution within the hot-side flow volume of theexchanger, enters Hot-Side Housing 8 where it is cooled by thethermosyphons/heat pipes (illustrated in FIG. 2), enters the Hot-SideHousing Exit Vapor Belt 10, which collects the hot-side flow evenly fromaround the circumference of Hot-Side Housing 8, and exits though BoltedFlange 7. Cold fluid enters through Bolted Flange 6, enters Cold-SideHousing 5 where it is heated by the thermosyphons/heat pipes, and exitsthrough Bolted Flange 4. Bolted Flange 2 connects the Plenum Housing 3to Relief Valve Piping 1. For normal operation, the pressure reliefvalve remains closed. For abnormal conditions where operating pressureof the thermosyphons/heat pipes increases above acceptable levels, thepressure relief valve, pressure safety valve, or pressure relief systemwill release thermosyphon/heat pipe working fluid through Relief ValvePiping 1 to maintain pressure within pre-determined constraints.

FIG. 2 illustrates an internal view of a thermosyphon heat exchanger inaccordance with one embodiment. In the embodiment illustrated in FIG. 2,the cold-side connections are located on the opposite side of Cold-SideHousing 5 shown in FIG. 1. In one embodiment, all parts illustrated inFIG. 1 are also present in the embodiment illustrated in FIG. 2. Theembodiment illustrated in FIG. 2 also includes parts not illustrated inFIG. 1. The additional parts identified in FIG. 2 are Plenum Plate 12,Separation Plate 13, Thermosyphons/Heat Pipes 14, and Drain 15.

Plenum Plate 12 may be implemented as a plate to which thethermosyphons/heat pipes are welded, roll expanded, or otherwiseattached, and which may separate the upper plenum from the cold sideflow volume of the heat exchanger. Separation Plate 13 may beimplemented as a plate to which the thermosyphons/heat pipes are welded,roll expanded, or otherwise attached, and which may separate thecold-side flow volume of the exchanger form the hot-side flow volume ofthe exchanger. Thermosyphons/Heat Pipes 14 may be implemented asthermosyphons (wickless heat pipes) or heat pipes (which have a wick),which may pass through both Plenum Plate 12 and Separation Plate 13 suchthat they pass through both the hot-side and cold-side flow volumes ofthe exchanger, and which may be open to Plenum Housing 3.Thermosyphons/Heat Pipes 14 may be welded, roll expanded, or otherwiseattached and sealed at Plenum Plate 12 and Separation Plate 13,resulting in three, separate, fully-sealed sections of the exchanger,which are the hot fluid section, the cold fluid section, and thethermosyphon/heat pipe working fluid section. The working fluid sectionincludes the internal volumes of the Thermosyphons/Heat Pipes 14 and theupper plenum to which they are open. Drain 15 may be implemented as anopening near the bottom of the hot-side flow volume, may include anopening in the Hot Side Housing Inlet Vapor Belt 11, and may alsoinclude a removable cap, bolt, or other attachment.

In one embodiment, the operation of the additional parts identified inFIG. 2 is as follows. In one embodiment, Plenum Plate 12 may be weldedor otherwise connected to Cold-Side Housing 5 and Plenum Housing 3, andseals the cold side of the exchanger from the upper plenum. In oneembodiment, Separation Plate 13 may be welded or otherwise connected toCold-Side Housing 5 and Hot-Side Exit Vapor Belt 10, and seals the coldside of the exchanger from the hot side of the exchanger.Thermosyphons/Heat Pipes 14 may remove heat from the hot-side fluid flowand transport it to the cold-side fluid flow via the evaporation (in thehot-side fluid section) and condensation (in the cold-side fluidsection) of an internal working fluid within Thermosyphons/Heat Pipes14. The resulting flow field inside Thermosyphons/Heat Pipes 14 may besuch that evaporated vapor rises from the hot-side flow section and intothe cold-side flow section, while condensing liquid moves in theopposite direction due to the force of gravity, capillary action, or acombination of both gravity and capillary action. The working fluid andmass per unit volume of working fluid in Thermosyphons/Heat Pipes 14 maybe selected for maximum heat transfer within the target operatingtemperature range of the application. Additionally, the working fluidand mass per unit volume of working fluid in Thermosyphons/Heat Pipes 14may be selected such that heat transfer is essentially prevented (e.g.,all or almost all of the heat transfer ceases) above or belowpre-determined temperatures via the dry-out temperature (for uppertemperature limit) and/or freezing temperature (for lower temperaturelimit) of the working fluid at the selected mass per unit volume inThermosyphons/Heat Pipes 14. Drain 15 may serve as a mechanism forremoving accumulated liquid from the hot-side flow volume, for example,due to the use of cleaning liquids or spraying of water to cleanThermosyphons/Heat Pipes 14.

In one embodiment, the hot connections and hot housing vapor belts shownin FIGS. 1 and 2 are specifically designed for uniform flow distributionand low pressure loss. The hot housing inlet vapor belt may providecontrolled diffusion of the flow from the hot inlet connection, alongwith a circumferential feed to the thermosyphons/heat pipes, and alsoforce fluid evenly into the center of the tube bundle. The hot housingexit vapor belt may pull flow circumferentially from the tube bundle,and the extension of the hot housing into the hot housing exit vaporbelt may provide for more uniform pressure loss around thecircumference, both of which contribute to uniform flow.

For ease of reference, the embodiment illustrated in FIGS. 1 and 2 isreferred to as a “first” embodiment, but persons of ordinary skill inthe art would recognize that such first embodiment includes variationsin implementation and operation. In the first embodiment, a commonthermosyphon/heat pipe plenum is positioned at the top end of thethermosyphons/heat pipes, and includes hot and cold fluid connections asillustrated in FIGS. 1 and 2.

Another embodiment of the subject invention, referred to as a “second”embodiment for ease of reference, may include the addition of a centerplenum within the separation plate, such that the thermosyphons/heatpipes are no longer continuous between the hot-side flow volume and thecold-side flow volume, and such that the additional plenum space betweenthe hot-side flow volume and the cold-side flow volume providesadditional thermal isolation between the hot and cold sides of theexchanger. In this second embodiment, the upper and lowerthermosyphons/heat pipes may be aligned or not aligned, and may be ofsimilar cross section or different cross section, as necessary tooptimize internal fluid flow within the thermosyphons/heat pipes, and/ormaximize heat transfer. Such an arrangement may also be accomplished bycross-drilling the separation plate such that the tubes are connected bythe cross-drilled holes. This second embodiment may also be used toaffect a loop heat pipe design via use of inverter ducting or ducting toseparate the condensed liquid from the vapor for each thermosyphon/heatpipe built into the center plenum.

Another embodiment of the subject invention, referred to as a “third”embodiment for ease of reference, may include the addition of a bottomplate/plenum assembly that connects the bottom of the thermosyphon/heatpipes, to allow for re-distribution of condensed thermosyphon/heat pipeworking fluid among the thermosyphons/heat pipes, and to provideresistance to lateral displacement of the tubes.

Another embodiment may include the first, second, or third embodiment,for example, wherein either inlet vanes and/or internal flow baffles,which may be removable via access through the inlet and/or exitconnections, may be used to effect more uniform flow distribution,including on either or both hot and cold side flows, in any number andany combination. Internal baffles may also be used to secure thethermosyphons/heat pipes from lateral motion caused, for example, byimpinging flow from the hot inlet.

Another embodiment may include the first, second, or third embodiment,for example, wherein the holes in the top surface of the plenum platehave a rounded edge to facilitate condensate return. For the secondembodiment this may also be applied to the plate at the bottom of thecenter plenum.

Another embodiment may include the first, second, or third embodiment,for example, wherein the tube pattern may be triangular or any geometricpattern known in the art for a heat exchanger tube array design.

Another embodiment may include the first, second, or third embodiment,for example, wherein the separation plate may be curved, bowl-shaped, orhemispherical to effect a more efficient pressure vessel.

Another embodiment may include the first, second, or third embodiment,for example, wherein the direction of flow for the hot and cold fluidsmay be in either direction, or combination of directions.

Another embodiment may include the first, second, or third embodiment,for example, wherein the thermosyphons/heat pipes are not circular incross section, and/or which utilize textured or finned surfaces toimprove heat transfer, or for any thermosyphons or heat pipes known inthe art.

Another embodiment may include the first, second, or third embodiment,for example, wherein the hot-side housing and vapor belts, along withthe cold-side housing, may have any manner, orientation, andconfiguration for their respective inlet and exit flows, or where eitherof both vapor belts are not required to be used in the design, and thehot side flanges are directly on the hot side housing. For example, thehot-side inlet vapor belt may be eliminated, and the hot-side housingextended to near or past the bottom of the thermosyphons/heat pipes,with connecting flange located on the bottom of the hot-side housing, toallow for piping the hot-side inlet directly into the bottom of thehot-side housing from underneath the exchanger.

Another embodiment may include the first, second, or third embodiment,for example, wherein any component or part of a component may beinsulated to limit heat transfer from one component to another or to theenvironment.

Another embodiment may include the first, second, or third embodiment,for example, wherein a plate may be welded or otherwise attached on topof the plenum plate, which contains holes of diameter less than that ofthe thermosyphons/heat pipes, to allow for more even fill duringcharging, to reduce tube-to-tube interactions during operation(including re-distribution of working fluid between tubes), and/or toreduce velocities and mixing in the upper plenum when in operation.

Another embodiment may include the first, second, or third embodiment,for example, wherein a hopper system is included as part of the hotinlet and/or hot exit vapor belts, to collect particulate matter fromthe hot-side flow.

In one embodiment, a thermosyphon/heat pipe heat exchanger is providedto leverage the high surface area-specific heat transfer rates ofthermosyphons/heat pipes, to effect a compact and low-cost heatexchanger design, relative to traditional heat exchangers. Within thethermosyphon/heat pipe exchanger, a plenum located at the top end of thethermosyphons/heat pipes, to which the thermosyphons/heat pipes areopen, allows for reduced cost and time for thermosyphon/heat pipecharging as the thermosyphons/heat pipes can be simultaneously chargedwith a uniform charge, and which for vacuum charging allows for lowervacuum requirements while maintaining acceptable thermosyphon/heat pipeperformance as the plenum provides a volume to contain non-evacuatedgases. This also allows for economical field-adjustment of thethermosyphon/heat pipe charge, and provides a volume for collection ofnon-condensable gases formed by reaction of the thermosyphons/heat pipematerials with the thermosyphon/heat pipe working fluid, without impactto the performance of the thermosyphons/heat pipes, such thatpreviously-unacceptable low-cost materials can then be used withoutnegative impact to the performance of the heat exchanger.

In one embodiment, a pressure relief valve, safety relief valve, orpressure relief system may be positioned on the plenum described above,which allows for reduction in thermosyphon/heat pipe design pressure inhigh temperature applications, and a corresponding reduction inthermosyphon/heat pipe wall thickness which both increasesthermosyphon/heat pipe heat transfer and reduces cost. This featureallows for implementation of pressure and temperature limits on thethermosyphon/heat pipe working fluid, and allows for independent designcontrol over both the working fluid charge and the dry-out temperature,unlike sealed thermosyphon/heat pipe systems where the dry-outtemperature is determined only by working fluid and charge. This valvemay also be of the pressure safety valve type, with available manualoperation for use when charging the thermosyphons/heat pipes, else anadditional manual valve may be placed directly on the plenum, forexample, for the purpose of charging the thermosyphons/heat pipes.

In one embodiment, the working fluid and charge of thethermosyphons/heat pipes may be set to place the freezing temperatureand/or dry-out temperature of the thermosyphon/heat pipe working fluidto prevent further heat transfer above the dry-out temperature or belowthe freezing temperature. For the case of the dry-out temperature, thismay be done to protect the exchanger cold-side fluid against overheatingor decomposition, or in some cases to avoid vaporization of thecold-side fluid.

In one embodiment, the relief pressure may be set below, at, or abovethe dry-out temperature of the selected working fluid and charge. Thus,the relief pressure setting and/or the dry-out temperature may be setsuch that the cold-side fluid remains at or below the maximum allowabletemperature.

One embodiment enables thermal isolation of the exchanger hot and coldfluids, such that minimal heat transfer occurs directly between thefluids and substantially all heat transfer is performed and controlledby the thermosyphons/heat pipes.

Implementations of the subject invention exhibit inherent low pressureloss on both sides of the heat exchanger, due to low fluid velocitiesand minimal requirements for pressure loss to increase heat transfer.Also, embodiments of the subject invention exhibit uniform flowdistribution though the exchanger, with the provision to include inletguide vanes and/or internal baffles as needed to further improve theflow distribution. Internal baffles may also be used as a means tosecure the thermosyphons/heat pipes against lateral motion caused byimpingement of flow from the hot inlet, or other sources of excitation.

In addition to measuring fluid flows, pressures, and temperatures inheat exchangers, embodiments of the subject invention provide for simpleimplementation of measurement of both the pressure and temperature inthe thermosyphons/heat pipes, thereby ensuring proper charge, operatingpressure margin, and allowing for identification of the degree to whichnon-condensable gases exist in the thermosyphon/heat pipe fluid volume.

Embodiments of the subject invention provide multiple features for easeof cleaning and maintenance. In one embodiment, with hot inlet and exitpiping removed, direct access may be provided through the hot inlet andexit connections for cleaning of the hot side heat transfer surfaces ofthe thermosyphons/heat pipes, where particulate matter, soot, oil,scale, or other deposits may form, that reduce the heat transfer of theexchanger surfaces. Such cleaning may be performed via chemical agent,or pressure cleaning with liquid. This feature may be further enhancedvia use of a square tube pattern for the thermosyphon/heat pipe array,thereby allowing direct use of mechanical cleaning tools via theresulting straight tube gaps (cleaning channels) across the entire widthof the exchanger. A drain may be positioned at the bottom of theexchanger housing to allow evacuation of cleaning liquids and foulingdebris removed from the heat transfer surfaces. For more completecleaning, access features may be incorporated into the hot housing tomore directly access the thermosyphons/heat pipes. In addition, inaccordance with one embodiment the heat exchanger design is well-suitedfor acoustic on-line cleaning.

Implementation of one embodiment results in low thermal stresses in allcomponents of the exchanger. The thermosyphons/heat pipes may beconnected (via welding or roll expansion, for example) to both the upperplenum plate and the separation plate, but are free to expand thermallyin the hot section of the exchanger, where thermal growth and thermalstress concerns are greatest, due to built-in clearance between thebottom of the thermosyphon/heat pipe tubes and the bottom of theexchanger. For the cold section, which may be completely welded, thehousing and thermosyphons/heat pipes may see similar thermal growth,thereby minimizing thermal stresses in this section of the exchanger. Inone embodiment, for applications where cold section thermal stresses areunacceptably high, an expansion joint may be used in the cold housing.

Applications of the subject invention include, but are not limited to adirect evaporator ORC power plants; a district heating heat exchangerfor heating of district water from high temperature waste heat sourcessuch as gas engines; a heat exchanger for heating of fluids other thandistrict water from high temperature waste heat sources such as gasengines; a heat exchanger for heating of volatile fluids such as fuelgas for power plants, or between volatile streams such as heaters usedin oil and gas production and processing; a heat exchanger forapplications for shell and tube or other conventional heat exchangers;and a heat exchanger for waste heat boiler applications, wherein anembodiment of the subject invention produces superheated or saturatedsteam, for process or power generation.

The foregoing description of possible implementations consistent withthe method and system disclosed herein does not represent acomprehensive list of all such implementations or all variations of theimplementations described. The description of only some implementationshould not be construed as an intent to exclude other implementations.For example, artisans will understand how to implement the system andmethod disclosed herein in many other ways, using equivalents andalternatives that do not depart from the scope of the system and methoddisclosed herein. Moreover, unless indicated to the contrary in thepreceding description, none of the components described in theimplementations are essential to the system and method disclosed herein.It is thus intended that the specification and examples be considered asexemplary only.

1. A heat exchanger comprising: a first bolted flange for receiving hotfluid into the heat exchanger; a hot-side housing inlet vapor beltconnected to said first bolted flange for distributing flow of said hotfluid within a hot-side flow volume of said heat exchanger; a first setof one or more heat pipes for cooling the distributed flow of said hotfluid; a hot side housing exit vapor belt for collecting hot-side flowevenly from around a circumference of a hot-side housing and fordelivering the cooled fluid to a second bolted flange connected to saidhot side housing exit vapor belt so that the cooled fluid leaves theheat exchanger through said second bolted flange; a third bolted flangefor receiving cold fluid into the heat exchanger; a second set of one ormore heat pipes for heating said cold fluid; a fourth bolted flange forreceiving the heated fluid so that the heated fluid leaves the heatexchanger through said fourth bolted flange; and a fifth bolted flangefor connecting a plenum housing to a relief valve piping; wherein saidrelief valve piping is connected to a pressure relief valve, pressuresafety valve, or pressure relief system that remains closed duringnormal operation of the heat exchanger and opens to maintain pressurewhen operating pressure of the first and second set of heat pipesincreases above a pre-determined limit for continuous operation of theexchanger.
 2. The heat exchanger of claim 1, wherein the first set orthe second set of heat pipes comprises one or more heat pipes with awick.
 3. The heat exchanger of claim 1, wherein the first set or thesecond set of heat pipes comprises one or more wickless heat pipes. 4.The heat exchanger of claim 1, further comprising a plenum plateattached to said second set of heat pipes and separating a plenum fromcold side flow volume of the heat exchanger.
 5. The heat exchanger ofclaim 4, wherein the second set of heat pipes are open at the top andopen to said plenum by passing through said plenum plate or by holes inthe plenum plate,
 6. The heat exchanger of claim 1, further comprising aplenum plate connected to a cold-side housing and the plenum housing. 7.The heat exchanger of claim 6, wherein said plenum plate seals a coldside of the heat exchanger from an upper plenum.
 8. The heat exchangerof claim 1, further comprising a separation plate connected to acold-side housing and the hot-side exit vapor belt.
 9. The heatexchanger of claim 8, wherein said separation plate seals a cold side ofthe heat exchanger from a hot side of the heat exchanger.
 10. The heatexchanger of claim 8, wherein said separation plate contains an opening,hole, or a plenum within the separation plate, such that first set orthe second set of heat pipes connected to the separation plate is opento the opening, hole, or plenum within the separation plate.
 11. Theheat exchanger of claim 1, further comprising a plate attached to thebottom of the first set of heat pipes, and which contains an opening,hole, or a plenum within the plate, such that heat pipes connected tothe plate are open to the opening, hole, or plenum within the plate. 12.The heat exchanger of claim 1, wherein a hopper system is included aspart of the hot inlet or hot exit vapor belts, to collect particulatematter from the hot-side flow.
 13. The heat exchanger of claim 1,wherein said first and second sets of heat pipes form a single set ofcontinuous heat pipes.
 14. The heat exchanger of claim 1, wherein saidfirst and second sets of heat pipes are open to each other.
 15. A heatexchanger comprising: a first bolted flange open at the bottom of theheat exchanger for receiving hot fluid into the heat exchanger; a firstset of one or more heat pipes for cooling said hot fluid; a set ofsecond bolted flanges for receiving the cooled fluid so that the cooledfluid leaves the heat exchanger through said set of second boltedflanges; a third bolted flange for receiving cold fluid into the heatexchanger; a second set of one or more heat pipes for heating said coldfluid; a fourth bolted flange for receiving the heated fluid so that theheated fluid leaves the heat exchanger through said fourth boltedflange; and a fifth bolted flange for connecting a plenum housing to arelief valve piping; wherein said relief valve piping is connected to apressure relief valve, pressure safety valve, or pressure relief systemthat remains closed during normal operation of the heat exchanger andopens to maintain pressure when operating pressure of the first orsecond set of heat pipes increases above a pre-determined limit forcontinuous operation of the exchanger.